1. Field of the Invention
This invention relates, in general, to sheet feeding devices and, in particular, to a new and useful sheet feed bench and to a method of feeding sheets off a stack thereof.
This invention concerns a sheet feed bench with two parallel sheet feed rails adjustable relative to one another, each of which has several blower jets directly above the level of the bench on their sides facing one another, which are connected or can be connected to a common source of compressed air, and with a single-sheet separator by which the bottom sheet is taken from a stack of sheets that can be refilled from the top.
The single-sheet separators of such sheet benches generally consist of a suction roll that has a number of radial suction holes and is provided with a sector-like vacuum chamber to which a suction fan is connected. Means of transport consisting of rolls or rollers, driven synchronously with the suction roll, are usually placed behind the suction roll and parallel to its axis, to receive the separated sheets and to transport them further. Such sheet feed benches are used, for example, to supply individual sheets from a stack of identical paper sheets at definite, preselectable time intervals, to packaging machines, printers, labelling machines, or the like. Compressed air is blown by the blower jets located in the sheet feed rails from both sides between the bottom sheets of a stack of sheets which results in the formation of at least a thin cushion of air between the individual sheets and thereby facilitates the singling of the sheets and makes it more reliable The front end of the bottom sheet is drawn in by suction by means of the suction roll, and is fed through a stationary stopper edge adjustable in height for different thicknesses of a vertical stopper placed above the suction roll, and is transported to the means of transport located beyond it, which then takes over the further transport of the separated sheet.
The formation of the air cushion between the bottom sheets of the stack of sheets is necessary to relieve the bottom sheet of the weight of the stack. Consequently, the size or weight of a stack that can be stored depends on the carrying capacity of the air cushion and on the nature of the formation of the air cushion in the area of the bottom sheet.
It has already been attempted to improve the quality of formation of the air cushion by increasing the blowing power, i.e., by increasing the supply of compressed air. However, it was found that this step alone cannot produce a significant improvement of the formation of the air cushion, because too much compressed air can escape from the edges of the stack of sheets, which is lost for the formation of the air cushion.